Gas turbine engines operate by passing a volume of high energy gases through a plurality of stages of vanes and blades, each having an airfoil, in order to drive turbines to produce rotational shaft power. The shaft power is used to drive a compressor to provide compressed air to a combustion process to generate the high energy gases. Additionally, the shaft power may be used to drive a generator for producing electricity, or to drive a fan for producing high momentum gases for producing thrust. In order to produce gases having sufficient energy to drive the compressor, generator and fan, it is necessary to combust the fuel at elevated temperatures and to compress the air to elevated pressures, which also increases its temperature.
A typical gas turbine engine is also used to power other systems in which the gas turbine engine operates. For example, gas turbine engines provide air for environmental control systems (ECS) that provide cabin air to the aircraft after sufficient conditioning. The air for the ECS is typically bled from the high pressure compressor. The siphoned compressor bleed air is typically routed from the compressor flow path, through a compressor case structure, through other components in the gas turbine engine, and out to the ECS. As such, the bleed air must pass through rotating and non-rotating components between the high pressure compressor and the ECS. Routing of the cooling air in such a manner incurs aerodynamic losses that require bleeding of an increased volume of air, thereby reducing the efficiency of the compressor and the gas turbine engine. There is, therefore, a continuing need to improve aerodynamic efficiencies in bleeding air from compressors within gas turbine engines, particularly at the point of departure from the compressor case structure.